Use the correct tornado import as suggested by @ivanov

IPython/frontend/html/notebook/handlers.py

@@ -29,7 +29,7 b' import time'
 import uuid
 import os
 
-import tornado
+from tornado.escape import url_escape
 from tornado import web
 from tornado import websocket
 
@@ -226,7 +226,7 b' class LoginHandler(AuthenticatedHandler):'
     def _render(self, message=None):        
         template = self.application.jinja2_env.get_template('login.html')
         self.write( template.render(
-                next=tornado.escape.url_escape(self.get_argument('next', default=self.application.ipython_app.base_project_url)),
+                next=url_escape(self.get_argument('next', default=self.application.ipython_app.base_project_url)),
                 read_only=self.read_only,
                 logged_in=self.logged_in,
                 login_available=self.login_available,